Balanced sound recording and reproducing system



Nov. 24, 1931.

R. J. POMEROY BALANCED SOUND RECORDING AND REPRODUCING SYSTEM 3 Sheets-Sheet 1 Inventor Boy I Pomeray Mam Nov. 24, 1931. R. J. POMEROY BALANCED SOUND RECORDING AND REPRODUCING SYSTEM Original Filed Oct. 3 Sheets Sheet 2 v 190 fpomeroy I fii-Zvrney W @Ew LMEW Nov. 24, 1931. R. J. POMEROY 1,833,373

' BALANCED SOUND RECORDING AND REPRODUCING SYSTEM Original Filed Oct. 26. 1927 3 Sheets-Sheet 5 [raven zbr P05 fpomeroy Patented Nov. 24, 1931 UNITED STATES PATENT OFFICE ROY J, POMEROY, OF HOLLYWOOD, CALIFORNIA, ASSIGNOR OF ONE HALF TO PARA- MOUNT PUBLIX CORPORATION, A. CORPORATION OF NEW YORK BALANCED SOUND RECORDING AND REPRODUOING SYSTEM Application filed October 26, 1927, Serial No. 228,711. Renewed April 18, 1981.

' This invention has to do with a balanced sound recording and reproducing system, and relates generally to a push-pull the reproduction of sound. A particular application of this invention involves the use of a photographic sound record, and the invention will be hereinafter described mainly in that connection, but without necessary limi-. tation thereto.

Broadly, the system consists in the obtaining of two concomitant complementary sound wave records or representations; and in final distortionless reproduction of the original sound therefrom by causing a diaphragm to vibrate under the combined influence of the two representations of the sound wave.

These sound wave representations each consist of a complete record or representation of the original sound Wave, but differ from one another in being complementary. That is to say, the outlines of the wave forms are identical, but the vertical displacement of one wave is positive while that of the other is negative, and vice versa; thus one always has a peak opposite a corresponding depression of the same outline on the other.

The system is carried out typically by providinga double amplifying system of the push-pull circuit, both channels being connected to a single three-wire microphone at the input end, and each being connected to separate sound wave recording means at the output end. Such circuits will each carry an undulating current representation of the sound Wave, differing only in that one is the complement of the other, as previously described. wave representations are made, this preferably being done photographically by causing the undulating current to vary the light falling upon a travelling film. Then by mak ing use of the varying light transmissivity of such films and photo-electric means, the two sound wave records may be reproduced as undulating electric currents, having the characteristics of the two original complementary current representations of the sound wave. These currents maybe conducted into further amplifying systems, the two separate outputs of which are connected to speaker or system for Sound records of these two sound,

.jOthel re roducing means so that the diaphragm is actuated by the combined action of the magnetic effects produced by the separately acting complementary current waves. It is so arranged, further,-that the diaphragm is pulled in one direction by the magnetic action of a maximum current peak in one Wave and is allowed to go in. that direction by a corresponding mimmum depression in the other; and then when this maxlmum peak is passed, the diaphragm is magnetically pulled back by the building up of the other wave to maximum value, instead of allowing it merely to come back of its own elasticity.

The advantages and features of my invention will be better understood from the following detailed descri tion, wherein I have particularly describe and illustrated the photographic type of sound record in connection with the invention, but it is to be understood that this particularization of the invention is no limitation thereto as many other forms may be utilized and are'contemplated within the spirit of the invention.

In the drawings:

Fig. 1 is a diagram illustrating circuits for making the photographic sound wave record.

Fig. 2 is a dia ram illustrating the method of sound repro uction from the record obtained as in Fig. 1.

Figs. 3 and 4 are diagrams illustrating typical manners in which the records can be made;

Fig. 5 is a diagram showing instantaneous images obtained in the method of Fig. 4.

With reference to Fig. 1, the numeral 20 indicates a three-wire microphone of the push-pull type, the carbon buttons of which are connected through wires 21 and 22 to the primary of transformer T, and the diaphragm 90 being connected with wire 23 through battery B to the center of the primary of transformer T. The secondary transformer T is connected into a duplex push-pull amplifying circuit 24, 25, the two channels 24 and 25 of which carry the current corresponding to the two sound wave representations previously described. Two separate output circuits 30, 31 and 32, 33 are brought out of circuit 24, 25,.

and these output circuits are connected to suitable recording means. Typically, for a photographic record, there may be provided glow tubes G andG connected in opposite polarity relation to the circuits 30, 31 and 32,

- one .tube to glow higher than the other, and

vice versa for equal voltages in the other direction. The same film F may be used to photograph the wave forms of both channels, by simultaneously photographing one wave on the upper half of'the film and the other wave on the lower half. Or, separate but synchronously travelling films may be used for each channel. When the film is developed, it will show two complementary sound wave records 37 and 38 having identical outlines but having a maximum image on one corresponding to a minimum image on the other, and so on. For the purpose of illustration the drawings show the two complementary sound wave records of a simple steady tone. It will be noticed that in the arrangement shown, with the base lines of the waves to ward the edges of the film and the images extending inward toward each other, that the outlines of the two waves are always parallel. Either wave, however, may be inverted from this position, as to the arrangement of Fig. 4, in which case the images of the two waves extend in the same direction from their base lines, and the slope of the outline of one wave is always the negative of the other. These relations hold in the same manner in the case of a complex or varying sound wave.

In Fig. 2 is shown the reproduction system corresponding to the record making system of Fig. 1. The record film F here passes before two light sensitive elements S and S, which intercept light from illuminants I falling upon the two records 37 and 38 and passing through to affect the sensitive elements S and S". These sensitive elements may be, for instance, photo-electric or selenium cells. Elements S and S are-connected intothe inputs of amplifying circuits 40 and 41. In this case, the drawing illustrates separate amplifying circuits using common batteries instead of theduplex push-pull circuit of Fig. 1. Either c'ircuit may be used, however, in' either case. The output of amplifying circuits 40 and 41 are connected by circuits '42, 43 and 44, 45, respectively, to separate windings 46 and 47 on opposite sides (if the armature 48, which is linked to the diaphragm of speaker H.

How the two complementary current waves, both representing the original sound wave, are obtained will be seen from refer ence to Fig. 1. When the diaphragm vibrates in one direction it causes an increase of presthe other circuit. Thus, a movement of the diaphragm in one direction operating to increase the current in one circuit and to decrease it in the other, and vice versa, a sound wave acting to vibrate the diaphragm causes a current wave in one circuit, and a complementary current wave in the other, the two having the relative characteristics previously explained.

These two concomitant representatives of the sound Wave are utilized to make possible a highly eflicient system of soundreproduction, with distortion reduced to a minimum, and with a positive push-pull action of the diaphragm of the reproducing unit. This action of the diaphragm may be easily understood from reference to Fig. 2, for when during one half of the cycle onecurrent wave increases by some amount to an above average value, and the other decreases by this same amount to a below average value, the winding in which the first current flows is most strongly magnetized and the armature 48 is pulled positively in that direction; and in the second half of the cycle the relative strengths of the two cm'rents tively in the opposite direction.

Distortion is. kept at an absolute minimum in every'part of the system. The three wire or push-pull type of microphone initially transforms the sound wave into current waves with the least possible distortion. The

' are reversed andthe armature is pulled posiadvantages of this type of microphone are well known in the art and need not be set out in detail here. By keeping the two representations of the sound wave. separated throughout the amplifying systems, photographic records, and inthe final windings of the reproducing unit, neither wave can influence or distort the other throughout the system, and the diaphragm is positively vibrated under the balanced resultant action of the two complementary waves.

In Figs. 3 and'4 I show different methods of making the sound records. In Fig. 3 the npmerals 50 and 50a represent lights with filaments 51 and 51a casting images upon the traveling film F by the lenses 52 and 52a, slits 53 and 53a being used if desired. The resultant images upon the film will be of a constant length but will vary in density and in spacing, density representing intensity of sound and spacing frequency. As before, I have shown in the drawings a sound record representing a simple steady current, the dark and light images corresponding respecsound records.

tively to the peaks and depressions of the sound wave representations.

In Fig. 4 is diagrammed a cathode ray tube arrangement for the photographing of the The electrodes are indicated at 60 and 61, and at 60a and 61a, respectively. Thecathode rays pass'through slits 62 and 62a, respectively, and play along. the luminiscent surfaces 63 and 63a, creating lines of light which are ordinarily straight. Two electro-magnets used with each tube, as 64 and 64a, respectively, are energized from circuits 65 and 65a carrying audio frequency currents, the line of light in the cathode ray tube may be fluctuated or bent away from its normal straight path. Considering only one of the cathode tubes, if a slit 66 is then I placed so that in the normal my position a portion of the beam of light appears in the slit, somewhat asillustrated at A. in Fig. 5; then as the cathode ray is deviated the image viewed through the slit by lens 67 will appear as a wedge which may have a fixed base at one 'end of the slit but is of varying length. The other tube is similarly arranged with a corresponding slit 66a and lens 67a. Succes-.

sive instantaneous images I and Ia obtained in the two slits are indicated at A, B and C in Fig. 5. It will be noticed that as one image la increases in length its normal position A, the other image I correspondin ly decreases in length. A film F positione to travel in front of the two slits and having the images of the slit cast upon it by lenses 67 and 67a will take a record of the two concomitant sound waves, which Will appear as two shaded bands having wavy upper lines which represent the sound character.

The drawings again show only wave forms representing a simple steady tone. I have here illustrated the previously mentioned arrangement in which the images of both waves extend in the same'direction from the straight base lines.

This invention embodies several unique applications of the push-pull principle. The first is the use of the photographic or other sound wave record having upon it two concomitant representations of the same sound wave, each a complete record in itself but the two differing from each other in the manner explained, both bein adapted to modulate electric currents, givlng to them their individual characteristics, and these complementary currents, although electrically separated, acting in magnetic conjunction to vibrate a diaphragm. Further, the means of obtaining a push-pull action on the diaphragm is a new feature of the system, as previously the output of push-pull amplifying circuits were connected together electrically, so that the waves would augment each other, thus without the balanced efiect obtained when the diaphragm is pulled first in one direction by one wave and then in the up devices which are connected into the amplifying circuits in the'same way as the photoelectric devices of Fig. 2.

' It is evident that the correspondin wave forms on the recordsdo not have to e mechanically opposite one another either on the photographic record or on the mechanical type of record; for the pick-up devices may be adjusted to the exact position of the record to obtain the proper relation between the two waves for final reproduction.

This system may also be used when it is desired to merely amplify sound or reproduce it at a distance, without making a permanent record. In this case the record'making and reproducing units areomitted, the balance of the system operating as before.

I claim:

1. In a balanced sound recording and reproducing system, a sound record having two concomitant complementary sound wave representations, each such representation being complete in itself.

2. In a balanced sound recording and reproducing system, a photographic sound record having two concomitant complementary sound wave representations, each such representation being complete in itself.

3. In a balanced sound recording and reproducing system, electrical amplifying circuits, means for impressing on said circuits two complementary sound current representations of a. sound wave, each such representation being complete in itself, and sound reproducing means acted upon oppositely by the two complete complementary sound currents.

4. Ina balanced sound recording and reproducing systcm electrical amplifying circuits, means for impressing on. said circuits two complementary sound current representations of. a sound wave, each such representation being complete in itself, and a single sound wave reproducing means actuated by the resultant magnetic action'of two complete complementary sound currents.

5. In a balanced sound recording and reproducing system, means for transforming a sound wave into two complementary sound current representations of the sound wave,

each such representation beingcomplete in itself, electrical amplifying circuits for- 1 I individually amplifying the complementary sound currents, and sound reproducing moans associated therewith and actuated by two complete complementary sound currents.

6.' In a balanced sound recording and reproducing system, two complementary sound records. each such record being complete in itself, electrical circuits, means for impressing upon said circuits two complementary sound currents representative of the two complementary sound records, and sound reproducing means acted upon oppositely by the two complementary sound currents.

7. In a balanced sound recording and reproducing system, electrical circuits, means for impressing on said circuits two complementary sound current representations of a sound wave, each such representation being complete in itself, and sound reproducing means acted upon oppositely by the two complete complementary sound currents.

8. In a balanced sound recording and reproducing system, electrical circuits, means for impressing on said circuits two complementary sound current representations of a sound wave, each such representation being complete in itself, and a single sound wave reproducing means actuated by the resultant magnetic action of two complete complementary sound currents.

In Witness that I claim the foregoing I have hereunto subscribed my name this 21st day of October, 1927.

ROYJ. POMEROY. 

